What is inside the box? The end of the movie!
The stills are from "Kiss me deadly", a 1955 "Mike Hammer/Mickey Spillane"-film which was directed by Robert Aldrich.
Apparantly the ending of the film was changed shortly after its debut in the USA. Because the film did bad business and some religious nuts objected to the immorality of it all, the final minute of the film was edited in a way that suggested that the Mike Hammer-character and his secretary/fuck-buddy actually died in the fiery inferno that is unleashed after "the box" is opened.
I think this is a very rare case of changing an already bleak "happy ending" to an even bleaker one to increase the box-office.
For decades the mutilated ending was heralded as a stroke of genius and it was even suggested that the bumpy editing inspired the French Nouvelle Vague.
This is very unlikely because it seems that the originally intended ending was kept intact for the international market!
Francois Truffaut clearly describes the full ending in his critique and I remember having videotaped the original ending off of German tv sometime in the late 80s or early nineties. (I hope this will remain the only "Truffaut and me"-sentence I will ever write).
It is quite ironic that many great American directors salivated over this lost ending and even constructed whole theories about it, while the rest of the world watched the full version. To top it all: The short ending is actually the better one!